Zarontin Shortage: What Providers and Prescribers Need to Know in 2026

Ethosuximide (Zarontin) remains the Level A, first-line agent for childhood absence epilepsy, backed by Class I randomized controlled trial evidence. Yet an increasing number of patients are reporting significant difficulty filling their prescriptions in 2026. This clinical briefing covers the current availability landscape, prescribing implications, evidence-based alternatives, and practical tools to help your patients maintain uninterrupted therapy.

Current Availability Status (2026)

As of early 2026, ethosuximide is not formally listed on the FDA or ASHP drug shortage databases. However, the practical reality is more nuanced. Ethosuximide occupies a paradoxical position in the pharmaceutical market: it is a highly effective, guideline-recommended medication treating a condition affecting a relatively small patient population. This creates a situation where the drug is technically available but functionally difficult for many patients to obtain.

Key contributing factors include:

• Manufacturer concentration: Pfizer manufactures brand-name Zarontin oral solution; only a small number of companies produce generic ethosuximide capsules. Industry consolidation since the 2010s has further reduced manufacturing redundancy.
• Low commercial priority: The small patient population (primarily pediatric patients with childhood absence epilepsy) reduces commercial incentive for manufacturers to maintain robust production capacity or inventory buffers.
• Wholesaler allocation patterns: When supply is constrained, distributors prioritize high-volume pharmacy accounts, leaving independent pharmacies and rural areas underserved.
• Low pharmacy stocking rates: Most retail pharmacies do not keep ethosuximide in stock. It is typically a special-order item requiring 1 to 5 business days to source.

Clinical Implications for Prescribers

Prescription Writing: Allow Formulation Substitution

Ethosuximide is available as 250 mg capsules and as a 250 mg/5 mL oral solution. When writing prescriptions, consider adding a note: "May substitute oral solution for capsules" or specifying both formulations as acceptable. This simple notation can dramatically expand available sources for patients and allows pharmacist substitution between formulations when one is out of stock.

Therapeutic Drug Monitoring When Supply Changes

It is reasonable to check trough ethosuximide levels (therapeutic range: 40–100 μg/mL) when patients change formulations, manufacturers, or pharmacies—particularly in patients with borderline seizure control. While bioavailability between formulations is generally comparable, individual pharmacokinetic variation exists. Valproic acid, carbamazepine, phenytoin, phenobarbital, and other enzyme-inducing antiseizure medications can all significantly affect ethosuximide levels.

Evidence-Based Alternatives When Ethosuximide Is Unavailable

The landmark NEJM randomized controlled trial (Glauser et al., N Engl J Med 2010) remains the primary evidence base for treatment decisions in childhood absence epilepsy:

• Valproic acid (Depakote): Equivalent efficacy to ethosuximide at 12 months (44% vs 45% freedom from treatment failure). More widely available. However, the valproic acid cohort had a significantly higher rate of treatment failure due to adverse events (33%) and negative effects on attentional measures compared to ethosuximide. Valproate is strongly contraindicated in women of childbearing potential due to teratogenicity (neural tube defects, cognitive effects). Requires hepatic and CBC monitoring.
• Lamotrigine (Lamictal): Significantly less effective for absence seizures in the same trial (21% freedom from failure at 12 months vs 45% for ethosuximide). However, lamotrigine has a favorable cognitive side effect profile and is the preferred option in women of childbearing age when valproate is contraindicated. Requires very gradual dose titration to minimize Stevens-Johnson syndrome risk.
• Clonazepam / Clobazam: Benzodiazepines may serve as short-term bridge therapy while ethosuximide supply is resolved. Not recommended for long-term monotherapy due to tolerance and dependence risk. Schedule IV controlled substances.

Special Populations: Key Prescribing Considerations

• Women of childbearing age: Valproic acid should be avoided. Lamotrigine preferred as alternative. Ethosuximide has limited teratogenicity data—counsel appropriately if patient becomes pregnant.
• Patients with mixed seizure types: Ethosuximide covers only absence seizures; valproic acid provides broader-spectrum coverage. Do not prescribe ethosuximide as the sole agent if the patient also has generalized tonic-clonic seizures.
• Renal/hepatic impairment: Ethosuximide should be used with extreme caution in patients with known liver or renal disease. Periodic urinalysis and liver function studies are advised.

Cost and Patient Assistance Resources

Cost can be a secondary barrier even when supply is available. Current pricing:

• Cash price: $200–$580 per month without insurance depending on formulation
• With GoodRx or SingleCare: as low as $33–$36 for generic ethosuximide
• Insurance: Most commercial plans cover generic ethosuximide without prior authorization as Tier 1 or Tier 2. Brand Zarontin may require PA.
• Pfizer RxPathways (1-844-989-7284): Patient assistance program for eligible uninsured or government-insured patients with income at or below 300% of Federal Poverty Level.

Tools to Help Your Patients Find Zarontin

Consider sharing medfinder for providers with your patients. medfinder calls pharmacies near a patient's location to find which ones have ethosuximide in stock. Patients provide their medication, dosage, and ZIP code—medfinder does the calling and texts results directly to the patient. This is particularly valuable for patients in rural areas or those with limited mobility.

Key Clinical Takeaways

• No formal FDA shortage exists as of 2026, but functional availability problems are widespread
• Allow formulation substitution on prescriptions to expand patient options
• Valproic acid is the most effective alternative but carries significant risks; lamotrigine preferred in women of childbearing age
• Monitor drug levels when patients change formulations or manufacturers
• Counsel patients to refill 1–2 weeks early and never stop abruptly

For a step-by-step provider guide to helping patients locate ethosuximide, see our companion article: How to Help Your Patients Find Zarontin in Stock: A Provider's Guide.